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Re: Does Xceed use industry standard compression algorithms ?

  •  05-23-2008, 5:45 AM

    Re: Does Xceed use industry standard compression algorithms ?

    Thanks a ton for your reply. 

    CharlesB:
    You have to determine whether the data is a zip file or raw compressed data. Your context suggests that this is raw compressed data.

    This is raw compressed data sent using UDP packets. 

    CharlesB:
      We cannot give you a definite answer because we don't know exactly how the data was compressed at its source.

    The source sending the compressed data provides a documentation which says:

    "All messages sent to us should be compressed using Xceed Zip Version 4.2
    All messages recevied should be uncompressed using Xceed Zip Version 4.2
    Xceed Zip Compression functionality if provided by Xceedzip.dll (COM Component 4.2) in class XceedCompressionClass which resides under XceedZipLib (Namespace). Methods used are Compress and Uncompress for compressing and decompressing data respectively."
     

    CharlesB:
    However, we would suggest that the data you have is compressed using the Deflate compression method and formatted using the ZLib format, which is a small header at the start of the data. This is what the streaming compression part of our Zip compression product uses by default.

    I have read the RFC 1950 http://www.faqs.org/rfcs/rfc1950.html which defines the header used in Zlib. But I was not able to understand what the header "00 33 30 30 32 37" means ? Is this a header specific to Xceed library ?

     

    CharlesB:
    You could use the ZLib library to decompress this data. Try feeding the data to ZLib by telling it it is compressed with deflate.

    I used the program http://www.zlib.net/zpipe.c listed on http://www.zlib.net/zlib_how.html and these are the two commands I gave:

    # g++ zpipe.c -lz
    # ./a.out -d < compressedpacket.1.txt > uncompressedpacket.1.txt
    zpipe: invalid or incomplete deflate data

    Zlib is telling me  invalid or incomplete deflate data.
     

    CharlesB:
    If the library has an option to look for the ZLib header, use it. If it doesn't work, try it again but without looking for the ZLib format and header.

    I can not find any such option in the  zlib manual http://www.zlib.net/manual.html
     

    CharlesB:
    If that doesn't work, try the other compression methods supported by Zlib.

    The manual http://www.zlib.net/manual.html talks about different window sizes. I am wondering what is the default window size used by Xceed and if that might have effect on inflating the data.

    I am wondering what how should I go about inflating this data. Any help would be very much appreciated.

    Thanks for your time,

    ----

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